International security is never out of the headlines. War and peace, military strategy, the proliferation of nuclear weapons and revisionist states remain central to the discussion, but concerns such as climate change, migration, poverty, health, and international terrorism have complicated the field. So what really matters: the traditional prioritization of state security or the security needs of individuals, humanity, and the biosphere? Using a broad range of international examples, Christopher Browning outlines the nature of the key debates about contemporary international security challenges, and discusses the inherent difficulties that exist in tackling them. He also asks to what extent such debates are infused with questions of power, politics, justice, morality, and responsibility.